I. Field of the Invention
This invention relates to a system for the removal of undesirable deposits within a patient's body and, more particularly, to a system for the application of highly-controlled, localized heat to precise points within a patient's body for the removal of undesirable deposits such as atheromatous plaque or a blood clot within arteries and for the removal of tumors.
II. Description of the Prior Art
There are a number of techniques known for remedying the problems associated with undesirable deposits within a patient's body such as atheromatous plaque within arteries. One such technique is balloon angioplasty which results in recanalization of the artery. This method is not well understood but it is believed that the plaque splits and gets partially embedded into the media of the vessel walls. There are a number of problems with this procedure since the plaque is not actually removed. One such problem is that the remnant of the procedure is a nidus for restenosis.
The problems associated with balloon angioplasty have led to the development of procedures for physically removing the plaque. Removal of the plaque can be achieved either by atherectomy (cut and retrieve) using an atherectomy device or by atherolysis (vaporization of plaque). The latter procedure has been preferred since it causes less trauma to the arterial wall and leaves behind a relatively smoother surface which may significantly reduce the incidence of restenosis. Moreover, such a device can also be used to recanalize a completely obstructed artery.
A number of devices are used for atherolysis with varying degrees of success. Such devices are physically coupled to a laser source with the laser beam being used as a heat source. One problem associated with the use of direct laser energy for atherolysis is that arterial wall perforation can result.
A hot tip laser probe, where the metal tip of a metal tip catheter is internally heated by an argon laser, has been used for atherolysis. The laser device is coupled to the metal tip with a thin optical fiber making the system compatible with catheters. A number of problems have been associated with the use of the hot laser tip probe. One problem is that the exact tip contact temperature is difficult (if not impossible) to monitor adequately, thereby potentially causing damage to the arterial wall when the tip is heated to temperatures that are too extreme. Another problem is that temperatures at the tip fluctuate, making it difficult to control removal of the plaque, particularly if it is calcified. Finally, the system is very expensive.
Another method to destroy atheromatous plaque involves injecting a hematoporphyrin into a patient for selective uptake into the atheromatous plaque. Light is delivered to the diseased vessel so that the light activates the hematoporhyrin and lysis of the plaque results.
Tumors are treated in several ways. Surgical removal of internal tumors in humans is a long established medical technique for removing undesirable growths within a patient's body. This technique often involves deep penetration and prolonged open procedures that increase patient trauma and sepsis hazard. The wide variety of techniques which have been developed include cryogenic and heated probes.
Hyperthermia is one such heating process which heats the tumor to 40.degree. C. and denatures the enzymes associated with the tumorous cell causing the tumor cells to lyse. Volume heating of a tumor is achieved with lasers. Nd-YAG lasers are preferred for their ability to deeply penetrate tissue because they are poorly absorbed by tissue and have a high level of scattering. Heating (or burning) is also employed for surgery and removing unwanted tissue such as warts.
A significant disadvantage of known heating techniques is that the heating device cools down slowly. The heating device must be cooled down before it is removed from a patient's body in order to prevent damage to adjacent tissue and to prevent damage to the catheter itself. Consequently, an extensive cooldown period before the device can be removed may result in excessive heating of tissue and lengthy treatment time.
New techniques and materials which obviate the problems of the known methods and devices are desired.